The present invention relates to a sealing system to prevent loss of fluid from an opening of a device through which a rotating member projects. More particularly, the present invention relates to such a sealing system in which the opening is sealed by a rotary shaft seal, a chamber receives any fluid leakage from the shaft seal, and a barrier seal prevents leakage of fluid from the chamber. Even more particularly, the present invention relates to such a sealing system in which barrier fluid is separated from the fluid so that the fluid is able to be returned to the device.
The prior art has provided numerous examples of sealing systems to prevent loss of process fluids from escaping from the interior of devices employing rotating shafts. As may be appreciated, the problem of leakage of process fluid is particularly exacerbated in devices such as compressors that operate at a higher pressure than their surroundings. Refrigerant leakage from a compressor of a refrigeration system can be particularly troublesome where the refrigerant is toxic or potentially destructive to the environment. In mixed gas refrigerant systems, although the refrigerant is not toxic, any leakage from the compressor will change the composition of the refrigerant because the constituents of a mixed gas refrigerant will leak in unequal amounts due to their different properties. Furthermore, the components of mixed gas refrigerants are expensive and any loss of refrigerant is a significant cost penalty to the process.
In the prior art, compressor assemblies for refrigeration systems are provided with integrated, compressors, motors and gear boxes. Refrigerant leaking from the compressor into the gear box is separated from gear oil contained in the gear box and drawn back into the suction side of the compressor. The gear box may be either hermetically sealed or vented.
An example of a sealed gear box is disclosed in U.S. Pat. No. 6,018,962. In this patent, the compressor assembly is housed in an air tight enclosure. Refrigerant leaking into the gear box mixes with gear oil and a mixture of refrigerant and gear oil collects in a sump of the gear box. The mixture is drawn through a demister element to separate the gear oil from the mixture under suction provided by the low pressure side of the compressor. The suction further draws the refrigerant from the demister element back to the low pressure side of the compressor.
U.S. Pat. No. 4,213,307 is an example of a compressor assembly having a gear box vented to a coalescing filter. The coalescing filter separates the refrigerant leakage from the gear oil. The gear oil, after separation from the refrigerant, is pumped back into a sump of the gear box by a jet pump. The refrigerant is drawn from the coalescing filter back to the low pressure side of the compressor. A separate oil pump is used to pump oil to bearings contained within the gear box and also to supply pressurized oil as a motive fluid to the jet pump.
The type of compressor assemblies, discussed above, have purpose-built enclosures and therefore, are not very applicable to large-scale installations in which the components are each provided with an enclosure and the components are separately installed on site. As will be discussed, the present invention provides a sealing system to seal a rotating shaft in which very little modification of the device to be sealed is returned and therefore, the system is applicable to both large and small-scale installations.
The present invention provides a sealing system to prevent loss of a process fluid from a device having a device opening and a rotating member operable for rotational movement within the device opening. The sealing system is provided with a rotary shaft seal to provide a seal between the rotating member and the device opening, thereby to inhibit leakage of the process fluid from the device. A chamber is connected to the device and aligned with the rotary shaft seal to recover leakage of the process fluid from the rotary shaft seal. In this regard, the term xe2x80x9cconnectedxe2x80x9d as used herein and in the claims encompasses both an integral formation such as with the housing of the device or other component and external connections of various types such as by welding. The chamber has an outlet port and opposed inner and outer openings to allow the rotating member to project through the chamber. A barrier seal is connected to the chamber, adjacent to the outer opening thereof. The barrier seal is provided with a bore to receive the rotating member and in inlet port in communication with the bore to inject a barrier fluid under pressure to prevent the escape of the process fluid from the outer opening of the chamber. Thus, the chamber also receives barrier fluid through the outer opening. At least one filter is in communication with the outlet port of the chamber to separate the barrier fluid from said process fluid. A return passageway is in communication with the at least one filter and is in communication with the device to return the process fluid to the device.
The device may be a compressor to compress the process fluid from an inlet pressure to an outlet pressure higher than that of an inlet pressure. The compressor is provided with an inlet section for receiving the process fluid at the inlet pressure and the return passageway is in communication with compressor so as to return the process fluid to the inlet section of the compressor. The compressor may be of the type that has an impeller to compress the process fluid entering the compressor from the inlet section. The rotating member of such a compressor may be an enlarged, cylindrical base element of an impeller, the cylindrical base element being located within the device opening, and a drive shaft element, projecting through the enlarged, cylindrical base element. The drive shaft element is connected to the impeller and extends through the barrier seal and the outer and inner openings of the chamber.
In any application of the present invention, the rotary shaft seal can be a labyrinth seal.
In the present invention, the barrier fluid can be a liquid upon introduction to the inlet port of the barrier seal thereby to produce within the chamber a mixture containing the liquid and a vapor comprising the process fluid. The at least one filter can therefore be a coalescing filter to coalesce the liquid from the mixture. The vapor of the mixture can also comprise barrier fluid vapor and a barrier fluid vapor trap can be interposed between the return passageway and the coalescing filter to separate the barrier fluid vapor from the vapor of the mixture. Additionally, the vapor of the mixture can further comprise water vapor and a water vapor trap can be interposed between the barrier fluid vapor trap and the return line to separate any water vapor from the vapor of the mixture.
In an application of the present invention to a compressor, the compressor can have a gear box from which the rotating member is driven. The barrier fluid can be gear oil to provide lubrication within the gear box and the bore of the barrier seal can be in communication with the gear box, opposite to the chamber, such that gear oil from the bore, at one end thereof, flows into the gear box.
In a sealing system of the present invention, a reservoir can be in communication with the coalescing filter to receive the separated barrier fluid liquid. A pump can be located between the reservoir and the inlet port of the barrier seal to pressurize the liquid.
The sealing system of the present invention can be applied to a compressor of a refrigeration system and the process fluid to be compressed can be a refrigerant. The refrigerant can be a mixed gas refrigerant.
As has been described above, the present invention provides a leak proof system in which a rotary shaft seal such as a conventional labyrinth seal is used in combination with a barrier seal, a filter and, when required, an adsorbent trap for water. The small amount of process fluid that will pass through the rotary shaft seal and mix with the barrier fluid is recovered and separated. The barrier fluid is returned to its reservoir and the process fluid is then transferred to an adsorbent bed where the refrigerant is dried, if necessary. The process fluid is then returned to the device without loss.
Since there is no loss in the system, no make-up of the barrier fluid is required. Also no auxiliary pumps are required by the system to return the captured refrigerant to the process. There is no specific type of enclosure required and the enclosures need not be integrated. As such, the present invention is applicable to large-scale installations. However, even in smaller installations, the elimination of the need for a specific integrated enclosure eases the complexity of maintenance operations for the compressor.